Prime Editing Mediated Generation and Correction of the mdx5cv Mutation Restores Dystrophin Expression in Myoblasts

Abstract

Duchenne muscular dystrophy (DMD) is caused by mutations in the DMD gene that abolish dystrophin expression. Prime editing enables precise genome modification without generating double-strand DNA breaks or requiring donor DNA templates. We established an in vitro prime editing workflow to generate and subsequently correct the mdx5cv mutation in mouse C2C12 myoblasts. Following optimization of engineered prime editing guide RNAs (epegRNAs) and PAM-flexible prime editors, wild-type cells were edited, clonally isolated, and genotyped. Mutation correction was then evaluated using optimized epegRNA designs. Two rounds of prime editing introduced the mdx5cv mutation into approximately 20% of alleles in C2C12 cells creating the mdx5cv C2C12 cell line. Clonal isolation yielded five homozygous mutant clones among 59 expanded colonies. Optimization studies identified an epegRNA containing a 16 nucleotide reverse transcription template and a 10 nucleotide primer binding site (RTT16/PBS10) as the most efficient design. Correction of the pathogenic allele reached approximately 26%, whereas longer PBS lengths reduced editing efficiency. In silico off-target analysis using Cas-OFFinder identified no candidate genomic loci with fewer than three mismatches for the spacer sequences used in either mutation generation or correction, suggesting a favorable predicted specificity profile. Corrected mdx5cv C2C12 myoblasts retained their capacity to differentiate into multinucleated myotubes. Representative Western blot analysis detected dystrophin protein expression in differentiated corrected mdx5cv myotubes, consistent with successful correction of the pathogenic mutation. These findings establish a robust prime editing platform for both the generation and correction of the mdx5cv mutation and provide proof of concept that precise correction of the pathogenic mutation is associated with restoration of dystrophin expression following myogenic differentiation.